Ganoderma tropicum (Jungh.) Bres., Annales Mycologici 8(6): 586 (1910)

Luangharn, Thatsanee, Karunarathna, Samantha C., Mortimer, Peter E., Hyde, Kevin D., Thongklang, Naritsada & Xu, Jianchu, 2019, A new record of Ganodermatropicum (Basidiomycota, Polyporales) for Thailand and first assessment of optimum conditions for mycelia production, MycoKeys 51, pp. 65-83 : 70-73

Ganoderma tropicum (Jungh.) Bres., Annales Mycologici 8(6): 586 (1910) Fig. 2

Description based on specimen from Thailand.

Basidiome. Sessile, dimidiate. Pileus shape. Semicircular to dimidiate or conks, up to 7-12 cm in length and 4-8 cm in width, up to 1.5 cm thick. Pileus surface. Dark brown (9F5) at the base, slightly brownish red (10C8) at center, reddish gray (10B8) extending to the margin, light yellow (1A5) to yellow (2A6) under basidiocarp with grayish yellow (4C7) to brown (6D7 to 6F6) close to tube layer on upper surface of pileus glabrous, weakly to strongly laccate, glossy and shiny, smooth, spathulate, shallow sulcate several layers thick, consistency furrows, thicker at the base than the margin, covered by a thin and hard crust, and light in weight when dried. Context trimitic, irregular cuticle cells, mostly light yellow (1A5) to yellow (2A6) close to crust, grayish yellow (4C7), brown (6D7 to 6F6) to dark brown (9F5), near the tubes, dense context layer, thick near the base, tough to break when dried. Hymenophore. Grayish yellow (4C7). Basidiospores. Mostly oblong ellipsoid and broadly ellipsoid with double wall (ganodermoid) at maturity, (7.3 –)7.6– 10.1(10.8) × (10.1)10.6-13.3(13.9) μm (x̄ = 9.1 × 12.2 μm, n = 50) (including myxosporium), (5.4 –)5.6– 8.3(8.6) × (8.3)8.4-12.5(12.9) μm (x̄ = 7.1 × 10.6 μm, n = 50) μm (excluding outer myxosporium), light brown (6D6-6D8), reddish brown (9F6) to dark brown (9F8), usually with one end tapering, and usually overlaid by a hyaline myxosporium. Tubes. 2-7 mm long, up to 80-170 µm wide, and sulcate at different levels. Stipe. Lateral, up to 1.5 cm thick, dark brown (9F5). Margin. reddish gray (10B8), up to 0.3-0.7 cm thick, round, tough and hard, thicker towards the margin. Pore. Angular, 4-7 per mm; pore diameter up to 65-120 µm. Pore surface Pale yellow (2A3) to light yellow (2A5) and brown (6D7) to dark brown (6F6) when touched. Hyphal system Generative hyphae up to 0.80-2.85 μm (x̄ = 1.45, n = 50) in diameter, colorless, thin-walled, some thick-walled, branched, with clamp connections; binding hyphae 1.00-3.10 µm (x̄ = 2.05, n = 50), colorless, thin-walled, much-branched, clamped; skeletal hyphae up to 1.45-4.25 μm (x̄ = 2.35, n = 50), colorless, thick-walled, unbranched or with a few branches in the distal end. Culture characteristics. Initially white (4A1) to yellowish white (4A2), pale yellow (4A3) when growing, become orange white (5A2), pale orange (5A3), light orange (5A4-6A5) and some reddish yellow (4A6) to dark brown (9F8) around the plugged circle of active mycelium after incubation for 3 weeks. Odor. Distinctive odor when fresh and dried.

Ganoderma tropicum is diagnosed as having a distinctly dimidiate, smooth, spathulate pileus, with a laccate or glabrous dark brown slightly brownish red upper surface, usually tough when dried; margin usually has a reddish gray surface, round and hard; pore surface pale yellow when young, light yellow when mature, and becoming brown or dark brown when bruised; basidiospores are described as ellipsoid, with size range of (7.3 –)7.6– 10.1(10.8) × (10.1)10.6-13.3(13.9) μm (including myxosporium), (5.4 –)5.6– 8.3(8.6) × (8.3)8.4-12.5(12.9) μm (excluding outer myxosporium); context trimitic, abundant generative hyphae with branches; thin-walled, binding hyphae; and skeletal hyphae with clamp connections.

Habitat.

Solitary on living Dipterocarpus species in deciduous forests.

Specimen examined.

Thailand, Chiang Rai Province, 19°48'24"N, 100°03'54"E, 836 m, October, 2017.

Optimal media conditions for mycelial growth and characteristics of mycelial cultures

In our study of the seven different agar media, mycelial growth (mm), growth rates (mm/day), and mycelial density were screened as an indication of favorable growth of Thai G. tropicum (Table 3). After 10 days of incubation, the agar surface was fully colonized with a white (6A1) to pale orange (6A2-6A3) mycelium. The best mycelium colony diameter was observed on PDA, MEA, and YPD media, following YMA, RBA, YEA, and CZA, respectively.

Mycelial morphology and colony color characteristics differed on each agar media (Fig. 3). For instance, the morphological characteristics of G. tropicum growth on CZA medium were expressed as a very scanty, cotton colony (Fig. 3A). The colony on YEA medium was similar to that of CZA, although YEA exhibited greater density and biomass (Fig. 3E). Mycelial morphological characteristics on MEA and YPD were similar; both were expressed as an abundant (5+) massive cottony colony with orange white to pale orange (6A1-6A3) colony (Fig. 3B, G). The PDA medium, by contrast, showed a somewhat abundant (4+) white cotton colony (Fig. 3C), which was a slightly dark golden yellow (5A7) colony after 18 days of incubation (Fig. 2E, F). Moderate colony growth (3+) was observed on RBA (Fig. 3D). Abundant white massive cottony mycelia, with a radius from the center towards the edge of the petri dish, were observed on the YMA medium (Fig. 3F). Furthermore, filamentous colonies were observed in all media, except for CZA and YEA.

Optimal pH conditions for mycelial growth

All pH values from 4-9 were suitable for promoting mycelium growth of G. tropicum , however, the most favorable pH range was shown to be pH 7-8, followed by pH 9 (Table 4).

Optimal temperature conditions for mycelial growth

Ganoderma tropicum mycelial growth increased when going up from 15-25 °C and 28 °C, after which it started to decline again, with the most suitable temperature for mycelial growth being between 25 °C and 28 °C. Although the mycelia could grow between 15-35 °C, growth appeared to be drastically suppressed at 15 °C and 35 °C (Table 5).